Vehicles may be fitted with evaporative emission control systems such as onboard fuel vapor recovery systems. Such systems capture and prevent release of vaporized hydrocarbons to the atmosphere, for example fuel vapors generated in a vehicle gasoline tank during refueling. Specifically, the vaporized hydrocarbons (HCs) are stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel. The fuel vapor recovery system may include one more check valves, ejector(s), and/or controller actuatable valves for facilitating purge of stored vapors under boosted or non-boosted engine operation. Regulations require that hardware pertaining to the fuel vapor recovery system be regularly assessed for the presence or absence of degradation.
Toward this end, U.S. Pat. No. 7,900,608 discloses diagnosing fuel vapor recovery system hardware during boosted engine operation. However, the inventors herein have recognized potential issues with such methodology. Specifically, the methodology relies upon monitoring pressure changes in the fuel vapor recovery system during boosted engine operation. However, depending on fuel tank size and fuel fill level, there may be varying timeframes for which boosted engine operation can pressurize or evacuate the fuel vapor recovery system in order to robustly assess such pressure changes to indicate the presence or absence of degradation. For hybrid electric vehicles, engine run-time may be infrequent, thus limiting opportunity to conduct such diagnostics. Furthermore, it is additionally recognized that boosted engine operation duration may frequently be less than the time frame to sufficiently pressurize or evacuate the fuel vapor recovery system, thus undesirably leading to aborted diagnostic routines and/or inconclusive results.
Accordingly, discussed herein, the inventors have developed systems and methods to address the above-mentioned issues. In one example, a method comprises while an engine of a vehicle is off and when a set of predetermined conditions are met, directing a positive pressure with respect to atmospheric pressure into an ejector system in order to communicate a negative pressure with respect to atmospheric pressure on a fuel system and an evaporative emissions system, and indicating that the ejector system is degraded responsive to the negative pressure not reaching a vacuum build threshold. In this way, when such an ejector system diagnostic cannot be conducted during an engine-on condition, the diagnostic may be conducted during engine-off conditions, which may increase completions rates for such a diagnostic and which may in turn reduce opportunities for release of undesired emissions to atmosphere.
As one example, directing the positive pressure into the ejector system may comprise commanding a routing valve to a second routing valve position to selectively couple a pump to the ejector system by way of an engine-off boost conduit. Alternatively, commanding the routing valve to a first routing valve position may selectively couple the pump to a vent line stemming from a fuel vapor storage canister positioned in the evaporative emissions system.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.